1. Field of the Invention
The present invention relates to the separation of metal ions in aqueous solutions. More specifically, the present invention relates to an electrocell and method for using the electrocell to separate trace ions from aqueous solutions. The United States Government has fights in this invention pursuant to Contract No. DE-AC09-89SR18035 between the U.S. Department of Energy and Westinghouse Savannah River Company.
2. Discussion of Background
There has been a need for a viable and relatively simple method and apparatus to separate trace metals from solutions thereof quantitatively. Solutions containing such metals range from seawaters to drinking water and other solutions that may contain metal ions.
Several known systems and techniques for performing trace metal analyses to indicate the presence and concentration of metals of interest are found in U.S. Pat. No. 3,904,487, U.S. Pat. No. 4,829,007, and U.S. Pat. No. 4,058,446. These systems, including the apparatus utilized in each, function according to their respective disclosures to achieve the results specified.
U.S. Pat. No. 4,058,446 discloses an improvement for an anodic stripping voltammetry system (ASV) for the measurement of concentration and presence of trace metals in seawater. In this disclosure, a combination electrode is made from a porous polyethylene cylinder having a coaxial base for receiving the following solution. A helically extending silver/silver chloride reference electrode is disposed on the outside of the cylinder and a platinum counter electrode is located in its bore. The porous polyethylene prevents chlorides from contaminating the reference electrode while the counter electrode drains off current.
U.S. Pat. No. 4,829,007 is directed to a process for detecting trace amounts of plateable metal in an aqueous fluid such as drinking water or industrial effluents. The pH of the fluid being treated is adjusted to the desired value. In a first electrochemical cell, the metal in the fluid is deposited upon a glassy carbon plating electrode held at a negative potential. The carbon electrode is de-plated in a second electrochemical cell. A porous solid test matrix impregnated with electrolyte is maintained proximate to the de-plating electrode (anode) and the cathode for retaining in solution the resulting metal ions formed from the de-plated metal. Upon completion of the de-plating step, a color indicator is added to the test matrix to provide an indication of the presence of the metal. Levels of lead as low as 5 ppb can be detected.
U.S. Pat. No. 3,904,487 discloses an apparatus and method of determining the presence and concentration of trace metals in seawater; anodic stripping voltammetry (ASV) method and apparatus are utilized. A tubular, mercury-graphite electrode is coupled to receive a flowing mercury solution; a thin film of mercury is deposited on the inner surface of this electrode after the plating potential is coupled. A solution of seawater containing trace metals is then pumped through this electrode and trace metals are reduced onto the activated mercury film on reconnecting of plating potential to the electrode. After a pre-determined time, a pulsed scanning potential gradient is applied across the two electrodes; individual types of trace metals are then selectively stripped (oxidized) and the magnitudes of the currents at these levels are monitored and are proportional to the concentration of the trace metals. The mercury film is then stripped away by increasing the scanning potential, a fresh film of mercury is then deposited and the electrode then is used on another sample solution containing trace metals.